A stem nut is a threaded nut that surrounds and threadingly engages the threads of a reciprocating or movable valve stem. Rotation of the stem nut causes axial movement of the valve stem.
Some stem nuts include an internal grease path for introduction of grease to grease or lubricate the mated threads of the stem nut and the valve stem.
Other stem nut and valve stem designs, however, do not provide an internal grease path. For example, motor operated valves used in the nuclear power industry are typically designed without internal grease paths included in the stem nuts. Re-lubrication of the mating thread area requires cycling the valve to an open position to expose the valve stem threads above the stem nut. While this may seem like a minor operation, many motor operated valves cannot be conveniently cycled without causing liquid inventories to flow.
Other valves having a valve stem and stem nut arrangement permit only insignificant exposure of the valve stem threads. The full movement of the valve stem may occur through only a quarter-turn of the stem nut, or some other short stroke. The short stroke does not sufficiently expose the valve stem threads in the mating area of the valve stem for the effective manual application of grease by a brush or other means.
Yet other valves having a valve stem and stem nut arrangement enable substantial exposure of the valve stem threads. Grease can be applied to the exposed valve stem threads. Warren, U.S. Pat. No. 2,816,566 discloses, for example, a valve having a valve stem and stem nut arrangement in which a portion of the valve stem immediately below the stem nut is normally exposed. This lower portion of the valve stem is made to pass through a cylindrical sleeve that loosely surrounds the valve stem portion. A fitting attached to the sleeve allows grease to be supplied to the sleeve for greasing the lower valve stem portion.
But even where valve stem threads can be exposed for application of grease, entry of valve stem threads into the stem nut can wipe much of this applied grease from the stem. Wiping of the grease by the stem nut may result in less than optimal coverage of the mating thread surfaces with grease.
Thus there is a need for an improved method of greasing the mated threads of a threaded connector, and in particular, an improved method of greasing the mated threads of a valve stem and a valve stem nut, that does not require an internal grease path in the stem nut, does not require movement of the stem valve relative to the stem nut, and does not rely only on greasing the threads of the valve stem outside of the stem nut.